Solid-state image pickup device, method of manufacturing solid-state image pickup device, and electronic apparatus

ABSTRACT

Disclosed herein is a solid-state image pickup device including a solid-state image pickup element operable to produce an electric charge according to the amount of light received, a lens disposed on the upper side of a pixel of the solid-state image pickup element, a protective film which covers the upper side of the lens and a surface of which is flattened, and a surface film which is formed at the surface of the protective film and which is higher in hydrophilicity than the inside of the protective film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state image pickup device, amethod of manufacturing a solid-state image pickup device, and anelectronic apparatus. More specifically, the invention relates to asolid-state image pickup device, a method of manufacturing a solid-stateimage pickup device, and an electronic apparatus in which deposition ofdust on an optical path during the manufacture of the device orapparatus is prevented.

2. Description of the Related Art

There has been disclosed a technology in which a flattening film lowerin refractive index than microlenses of a solid-state image pickupelement is disposed on the microlenses, and the flattening film is usedas a protective film to thereby prevent deposition of dust and toprovide hermetic seal between the solid-state image pickup element and atransparent substrate, thereby reducing reflection at interfaces andincreasing the sensitivity of the image pickup element.

For example, Japanese Patent Laid-Open No. Hei 6-232379 referred to asPatent Document 1 hereinafter describes a configuration in which atransparent flat film having water repellency and oil repellency isprovided at an outermost layer of a solid-state image pickup element. Itis shown that this configuration enables easy cleaning of dust or thelike deposited on the outermost layer of the solid-state image pickupelement. It is also shown that the transparent flat film has a lowsurface energy, so that contamination with dust or the like issuppressed.

Besides, Japanese Patent Laid-Open No. 2007-53153 referred to as PatentDocument 2 hereinfater describes a configuration in which a flat layerof a fluoro acrylic resin is formed on microlenses of a solid-stateimage pickup element, and the surface of the flat layer is roughened. Itis shown that by this configuration it is possible to reduce or obviatedeposition of dust or foreign matter during later steps such as dicingor module fabrication.

Furthermore, Japanese Patent Laid-Open No. 2007-53324 referred to asPatent Document 3 hereinafter describes a structure of a solid-stateimage pickup element in which a fluorine-containing resin material layeris provided on microlenses of the image pickup element, a resin layer isprovided over the fluorine-containing resin material layer, and atransparent substrate is disposed over the resin layer. It is shown thatthis structure makes it possible, by appropriately determining therefractive indexes of the layers, to reduce reflected components of thelight incident on the solid-state image pickup element, and promises anincreased sensor sensitivity. It is also shown that, by eliminating anair layer between the solid-state image pickup element and thetransparent substrate, deposition of dust or the like duringtransportation of a solid-state image pickup device is prevented.

SUMMARY OF THE INVENTION

However, in the case where a transparent flat film having waterrepellency and oil repellency is provided at an outermost layer of asolid-state image pickup element, washing water used at the time ofwafer dicing is not sufficiently distributed to the wafer surface and,therefore, it may be impossible to achieve satisfactory removal of dust.In addition, when the surface of a flat layer provided on microlenses isroughened, a preventive effect on dust deposition may not be obtained.

Thus, there is a desire to prevent deposition of dust during manufactureof a solid-state image pickup device, thereby providing a desiredproduct having excellent optical characteristics.

According to an embodiment of the present invention, there is provided asolid-state image pickup device including a solid-state image pickupelement operable to produce an electric charge according to the amountof light received, a lens disposed on the upper side of a pixel of thesolid-state image pickup element, a protective film which covers theupper side of the lens and a surface of which is flattened, and asurface film which is formed at the surface of the protective film andwhich is higher in hydrophilicity than the inside of the protectivefilm.

In this embodiment, in a configuration wherein a lens is disposed on theupper side of each pixel of a solid-state image pickup element and thelenses are covered with a protective film having a flattened surface, asurface film higher in hydrophilicity than the inside of the protectivefilm is provided at the surface of the protective film. The hydrophilicnature of the surface of the protective film promises uniformdistribution of washing water to the surface of the protective filmduring a manufacturing process, whereby dust can be removed assuredly.

While the surface film higher in hydrophilicity than the inside of theprotective film is provided at the surface of the protective film, asurface film lower in hydrophobic nature than the inside of theprotective film may also be provided, to yield a similar effect to theabove-mentioned. Specifically, where the protective film is formed froma fluorine-containing resin, the surface film is lower in fluorinecontent than the inside of the protective film.

The protective film may be formed from a fluorine-containing silanecompound, a fluorine-containing siloxane resin, or a fluorine-containingsiloxane resin admixed with silica particulates having voids therein.

Examples of the surface film include a film or layer formed bysubjecting the protective film to a plasma treatment using anoxygen-containing gas.

According to another embodiment of the present invention, there isprovided a method of manufacturing a solid-state image pickup device,including the steps of forming a lens on the upper side of a pixel of asolid-state image pickup element, covering the lens with a protectivefilm and flattening a surface of the protective film, and forming at thesurface of the protective film a surface film which is higher inhydrophilicity than the inside of the protective film.

In this embodiment, since the surface film higher in hydrophilic naturethan the inside of the protective film is provided at the protectivefilm, washing water is uniformly distributed to the surface of theprotective film during cleaning of the protective film surface usingwashing water in the manufacturing process of the solid-state imagepickup device. Consequently, dust can be removed securely.

According to a further embodiment of the present invention, there isprovided an electronic apparatus including a solid-state image pickupdevice, and a signal processing unit operable to process a signal basedon an electric charge produced by the solid-state image pickup device.The solid-state image pickup device includes a solid-state image pickupelement operable to produce an electric charge according to the amountof light received, a lens disposed on the upper side of a pixel of thesolid-state image pickup element, a protective film which covers theupper side of the lens and a surface of which is flattened, and asurface film which is formed at the surface of the protective film andwhich is higher in hydrophilicity than the inside of the protectivefilm.

In this embodiment, in an electronic apparatus using a solid-state imagepickup device wherein a lens is disposed on each pixel of a solid-stateimage pickup element and the lenses are covered with a protective filmhaving a flattened surface, a surface film higher in hydrophilic naturethan the inside of the protective film is provided at the surface of theprotective film. Due to the presence of the surface film, uniformdistribution of washing water to the surface of the protective filmduring the manufacturing process is promised by the hydrophilic natureof the surface of the protective film. Accordingly, dust can be removedassuredly.

Thus, according to embodiments of the present invention, it is possibleto prevent dust deposition during manufacture of a solid-state imagepickup device, particularly, during a wafer dicing step, and to providea desired product having excellent optical characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of an example of a solid-state imagepickup element constituting a main part of a solid-state image pickupdevice according to an embodiment of the present invention;

FIG. 2 is a schematic sectional view illustrating a package mountingexample of the solid-state image pickup device according to thisembodiment;

FIG. 3 is a schematic enlarged view of part A of FIG. 2;

FIG. 4 is a schematic plan view of a configuration example of a chip inthe solid-state image pickup device;

FIGS. 5A to 5G are schematic sectional diagrams for illustrating aprocess flow (No. 1) of a method of manufacturing a solid-state imagepickup device according to an embodiment of the invention;

FIGS. 6A to 6G are schematic sectional diagrams for illustrating aprocess flow (No. 2) of a method of manufacturing a solid-state imagepickup device according to an embodiment of the invention;

FIGS. 7A and 7B are diagrams showing the results of investigation ofvariation of contact angle with time;

FIG. 8 is a table showing the results of visual checking of wettabilityin a dicing treatment;

FIGS. 9A to 9C show the surface state upon a surface treatment;

FIG. 10 is a table showing an example of element concentration ratiosaccording to the presence or absence of a surface treatment of aprotective film;

FIGS. 11A to 11D are schematic diagrams for illustrating another exampleof microlenses; and

FIG. 12 is a block diagram showing a configuration example of an imagepickup apparatus as one example of an electronic apparatus according toan embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, a mode for carrying out the present invention (hereinafter,referred to as “embodiment”) will be described below. The descriptionswill be made in the following order.

1. Structure of solid-state image pickup device (an example of plan-viewstructure of main part, an example of mounting of package, an example ofconfiguration on the upper side of pixel, and an example of plan-viewconfiguration of chip)2. Method of manufacturing solid-state image pickup device (examples ofprocess flow, No. 1 and No. 2 thereof)3. Investigation of effects of the embodiment (contents ofinvestigation, results of investigation, and elemental analysis ofprotective film and surface film)4. Comparison between the related art and the embodiment (comparisonbetween Patent Document 3 and this embodiment)5. Examples of application to various microlenses (spherical, aspheric,rectangular and diffraction examples)6. Electronic apparatus (example of application to image pickup device)

<1. Structure of Solid-State Image Pickup Device>

[Plan-View Structure of Main Part of Solid-State Image Pickup DeviceAccording to this Embodiment]

FIG. 1 is a schematic plan view for illustrating an example of asolid-state image pickup element constituting a main part of asolid-state image pickup device according to this embodiment. Thesolid-state image pickup element 20 includes a plurality of pixels 10,vertical signal lines VDL, a vertical selection circuit 11, a horizontalselection/signal processing circuit 12, and an output circuit 13.

The plurality of pixels 10 are arranged in a matrix pattern on asemiconductor substrate such as a silicon substrate. Each of the pixels10 has a light receiving part (photodiode) operable to produce anelectric charge according to the amount of light received, and aperipheral circuit including various transistors.

Each of the vertical signal line VDL is a wiring for sending a signalaccording to the electric charge taken in by each pixel 10 to thehorizontal selection/signal processing circuit 12, and is arrayed alongthe vertical direction in the matrix arrangement of the pixels 10. Thevertical selection circuit 11 is a circuit for selecting the pixels 10on a row basis, and performing a sequential scan along the verticaldirection.

The horizontal selection/signal processing circuit 12 is a circuit whichselects the pixels 10 on a column basis and performs sequential scanalong the horizontal direction, and is a circuit for processing signalssent thereto through the vertical signal line VDL. The horizontalselection/signal processing circuit 12 sequentially selects the pixels10 arrayed along the horizontal direction, synchronously with the scanconducted by the vertical selection circuit 11. According to the orderof selections, the signals of the pixels 10 are sequentially sent to thehorizontal selection/signal processing circuit 12 through the verticalsignal lines VDL. The horizontal selection/signal processing circuit 12sends to the output circuit 13 the signals of the pixels 10 sequentiallysent thereto.

The output circuit 13 performs various signal processings on the signalsof the pixels 10 sequentially sent from the horizontal selection/signalprocessing circuit 12, and outputs the resulting signals.

[Package Mounting Example of Solid-State Image Pickup Device]

FIG. 2 is a schematic sectional view illustrating a package mountingexample of the solid-state image pickup device according to thisembodiment. The solid-state image pickup device 1 has a solid-stateimage pickup element 20 cut from a wafer after the finish of waferprocessing into a chip form, and a package 21 in which to mount thesolid-state image pickup element 20. The solid-state image pickupelement 20 is adhered and fixed to a mounting part on the inside of aframe part of the package 21, and a transparent substrate 23 is attachedto the frame part of the package 21 through a sealing resin 22. Here, anair layer (in some cases it may be filled with a gas such as an inertgas) is provided between the upper side of the solid-state image pickupelement 20 and the transparent substrate 23, according to the height ofthe frame part, whereby the inside of the package is hermetically sealedin the state of a hollow structure. In this instance, if there is noproblem about the degree of cleanliness of the inside of the package 21,deposition of dust on the solid-state image pickup element 20 inside thepackage 21 would not be a problem.

[Example of Configuration of Part on Upper Side of Pixel]

FIG. 3 is a schematic enlarged view of part A of FIG. 2. This figureshows a schematic example of the configuration including the range fromthe surface of a semiconductor substrate S such as a silicon substrate,in the solid-state image pickup device 20, to the transparent substrate23. The semiconductor substrate S is provided with the light receivingparts PD, and, on the surface of the semiconductor substrate S, thevertical signal lines VDL are formed on both lateral sides of each ofthe light receiving parts PD. In addition, the vertical signal lines VDLare each covered by a light shielding film through an insulating filmtherebetween.

On the light shielding film, in-layer lenses IL are formedcorrespondingly to the positions of the light receiving parts PD, and afirst flattening film M1 having a flattened surface is formed on thein-layer lenses IL. On the first flattening film M1, color filters CFare provided correspondingly to the positions of the light receivingparts PD, and microlenses ML are formed on the color filters CFcorrespondingly to the positions of the light receiving parts PD.

In the solid-state image pickup device according to this embodiment, aprotective film 30 is provided which covers the upper side of themicrolenses ML and has a flattened surface. The protective film 30 is afilm which prevents the uppermost surfaces of convex protuberances ofthe microlenses ML from being exposed and the surface of which issubstantially flat. In addition, at the surface of the protective film30 is formed a surface film 31 which is higher in hydrophilicity thanthe inside of the protective film 30. Incidentally, while a film higherin hydrophilic nature than the inside of the protective film 30 is usedhere as the surface film 31, similar effects can also be obtained whenthe surface film 31 is a film which is lower in hydrophobic nature thanthe inside (bulk) of the protective film 30.

In this embodiment, for convenience of description, the surface film 31is described here to be distinct from the protective film 30. However,the surface film 31 is a film obtained by modifying the surface of theprotective film 30. In practice, therefore, the surface film 31 isformed of the same material as the protective film 30, and no interfaceis present between the surface film 31 and the protective film 30. Theabsence of any interface there ensures that needless reflection of lightwould not occur.

The protective film 30 is formed from a fluorine-containing silanecompound which is lower than the microlenses ML in refractive index andis good in transparency in the visible region. The protective film 30may also be formed from a fluorine-containing siloxane resin admixedwith silica particulates which have voids therein. The addition of thesilica particulates having voids therein ensures that the surface layerformed upon surface modification is higher in hydrophilicity and lowerin refractive index, as compared with those in the case where the silicaparticulates are not added.

In order that the surface film 31 provided at the surface of theprotective film 30 is higher in hydrophilicity than the inside of theprotective film 30, the surface of the protective film 30 is modified.For instance, the modification is carried out by activating the surfaceof the protective film 30. Specifically, for example, the surface of theprotective film 30 is modified by a plasma treatment using anoxygen-containing gas. The surface film 31 formed by such a modificationis lower in fluorine content than the inside (bulk) of the protectivefilm 30 formed from the fluorine-containing resin.

On the upper side of the protective film 30 (surface film 31) configuredas above, an air layer is present. Further, on the upper side of the airlayer is provided the transparent substrate 23, which is adhered with asealing resin (not shown). As a result, a solid-state image pickupdevice of a hollow structure is configured.

[Example of Plan-View Configuration of Chip]

FIG. 4 is a schematic plan view of a chip in the solid-state imagepickup element. The solid-state image pickup element 20 is provided witha light receiving region 40 in a central part of the chip, and with abonding pad region 50 in a peripheral part of the chip. In the lightreceiving region 40 are disposed a plurality of the light receivingparts PD in a matrix (columns and rows) pattern.

In the bonding pad region 50 are disposed a plurality of bonding pads51. The bonding pads 51 are connection terminals to which to connectbonding wires for connection between an external system and the circuitsin the chip. The bonding pads 51 are in connection with a peripheralcircuit (not shown) formed in the chip, and are connected to theexternal system through the bonding wires.

In the solid-state image pickup element 20 used in the solid-state imagepickup device according to this embodiment, the protective film isformed at least on the surface of the light receiving region 40, and theabove-mentioned surface film is formed at the flattened surface of theprotective film. Incidentally, the protective film (surface film) isopened (is provided with openings) where the surfaces of the bondingpads 51 are located.

A plurality of the solid-state image pickup elements 20 are fabricatedby use of a wafer at the same time, and, after the wafer process isfinished, the wafer is divided by wafer dicing, into the chips. Duringthe wafer dicing, swarf of the silicon substrate or the like isgenerated from the sections upon cutting by a dicing blade. For removalof the swarf, a cleaning liquid (e.g., washing water) is let flow duringthe dicing so that the swarf will not be left on the surfaces of thechips. In this embodiment, since the above-mentioned surface film isprovided at the surfaces of the solid-state image pickup elements 20 tobe diced into the chips, the cleaning liquid in the dicing process flowswhile making satisfactory contact with the whole area of the chipsurfaces due to the hydrophilic nature of the surface film. This ensuresthat the swarf is washed away together with the cleaning liquid, and theswarf is prevented from remaining on the chip surfaces, particularly onthe light receiving regions.

<2. Method of Manufacturing Solid-State Image Pickup Device> [ProcessFlow (No. 1)]

FIGS. 5A to 5G are schematic sectional diagrams for illustrating aprocess flow (No. 1) of a method of manufacturing a solid-state imagepickup device according to this embodiment. In the illustration of theprocess flow, schematic sectional diagrams pertaining to the lightreceiving region shown in FIG. 4 are shown on the left side, andschematic sectional diagrams pertaining to the bonding pad region shownin FIG. 4 are shown on the right side.

First, as shown in FIG. 5A, the color filters CF are disposed on thepixels in the light receiving region. Next, as shown in FIG. 5B, inorder to achieve flattening by burying the stepped portions present atthe surfaces of the color filters, a heat treatment at 180 to 230° C. isperformed for two to five minutes while using an acrylic thermosettingresin, for example, to thereby dispose a second flattening film M2.

Subsequently, a polystyrene-based positive photosensitive resistcontaining diazonaphtoquinone as a photosensitive agent (hereinafterreferred to as “resist”), for example, is applied to the substrate by aspin coating method at 800 to 200 rpm. Thereafter, a heat treatment at80 to 110° C. is carried out for 60 to 180 seconds by use of a hotplate, to obtain a film thickness of 0.3 to 1.0 μm.

Next, i-line exposure is conducted using a reduction projection exposuredevice, and then a developing treatment by a paddle method using, forexample, an aqueous 2.38% solution of TMAH (tetramethylammoniumhydroxide) is carried out for 40 to 120 seconds. As a result, a resistimage corresponding to the areas on the upper side of the pixels isobtained in the light receiving region.

Here, due to the presence of the diazonaphthoquinone photosensitiveagent in the above-mentioned resist, absorption in the visible region isprovided. Therefore, for example by use of UV rays such as the i-line,the photosensitive agent is decomposed, for enhancing the transmittancein the visible region.

Subsequently, a heat treatment at a temperature of not lower than theheat softening point of the resist is conducted, to obtain the shape ofthe microlenses ML, as shown in FIG. 5C. The heat treatment in thisinstance is preferably carried out, for example, on a hot plate at 140to 200° C. Incidentally, while a method of forming the microlenses ML bya heat treatment method has been described in this process flow, themicrolenses ML may be formed through transfer of the lens shape by anetch-back method.

Next, as shown in FIG. 5D, the protective film 30 is formed in the stateof burying the ruggedness of the microlens surfaces so that theuppermost surfaces of the convex protuberances of the microlenses MLformed correspondingly to the pixels in the light receiving region willnot be left exposed. In addition, the protective film 30 is so formedthat its surface is substantially flat.

In this embodiment, a fluorine-containing resin is used to form theprotective film 30, and, specifically, a fluorine-containing silanecompound is used as the fluorine-containing resin. Thefluorine-containing silane compound material is preferably afluorine-containing siloxane resin, of which the refractive index islower than that of the microlenses ML. In this embodiment, a protectivefilm 30 formed of the fluorine-containing siloxane resin is disposed tobe substantially flat, on the microlenses ML having a thickness of 0.4μm.

For example, in the case where a polystyrene-based material is used toform the microlenses ML, the refractive index of the material is about1.60. Taking into account the optical characteristics of the microlensesML, therefore, the refractive index of the fluorine-containing siloxaneresin is preferably 1.30 to 1.44.

In addition, in the case where a film of the fluorine-containingsiloxane resin is formed in the state of burying the ruggedness of thesurfaces of the microlenses ML and the thus formed film has asubstantially flat surface, the light condensing power of themicrolenses ML is lowered. As shown in FIG. 3, therefore, the in-layerlens IL may be incorporated between the light receiving part PD and themicrolens ML in the structure of the solid-state image pickup element20.

In this embodiment, for forming the protective film 30 on themicrolenses ML, the fluorine-containing siloxane resin is applied at1500 rpm in such a manner that a film thickness of 0.1 to 1.0 μm isattained after a baking treatment at 200° C. for five minutes.Incidentally, the film thickness of the protective film 30 here meansthe thickness as measured from the uppermost end of the protuberant formof the microlens ML to the substantially flat surface of the protectivefilm 30. Besides, the thickness of the protective film 30 is preferablyso set that the transmission of return light (reflected light generatedupon reflection of incident light by the surface of the semiconductorsubstrate) is minimized by an interference effect.

Incidentally, the conditions shown in the above description are merelyan example, and are not limitative. Various conditions such as theviscosity of material, the spinning speed, etc. may be modifiedaccording to differences in the thickness of the microlenses and thelike.

Subsequently, as shown in FIG. 5E, the positive photosensitive resist isapplied. The positive photosensitive resist may be, for example, aresist containing a novolak resin as a main constituent and containingdiazonaphthoquinone as a photosensitive agent. The positivephotosensitive resist is subjected to exposure and development so thatit covers the light receiving region and it is opened where the bondingpad parts and the like (e.g., the parts inclusive of scribe lines andthe like) are located. In this instance, the film thickness of thepositive photosensitive resist is so set that a residual film isobtained upon dry etching, which is a subsequent step.

Next, as shown in FIG. 5F, with the above-described photosensitiveresist as a mask, dry etching is conducted to etch away those portionsof a passivation film (e.g., P—SiN film or the like), the firstflattening film M1, the second flattening film M2, and the protectivefilm 30 formed of the fluorine-containing siloxane resin which arelocated in registry with the openings in the photosensitive resist.

The etching conditions to be used in this instance are, for example, asfollows.

Etching system: microwave plasma etching system

Magnetron power: 1100 W

Bias power: 40 W

Etching gas (1): SF₆ (flow rate: 300 SCCM)

Etching gas (2): O₂ (flow rate: 25 SCCM)

Electrode temperature: −30° C.

Pressure inside etching chamber: 2 Pa

In addition, the etching system is not limited to the microwave plasmaetching system, and applicable examples thereof include otherhigh-density plasma etching systems such as parallel plate RIE system,high-pressure narrow gap plasma etching system, ECR etching system,transformer-coupled plasma etching system, inductively coupled plasmaetching system, and helicon wave plasma etching system.

Further, the etching gas species are not limited to SF₆ and O₂, andother examples thereof include flon gases such as C₂F₆, C₃F₈, C₄F₈,CH₂F₂, CHF₃, etc., which may be used singly or may be used with O₂and/or such a gas as Ar, He, N₂ or the like added thereto.

Subsequently, as shown in FIG. 5G, the positive photosensitive resisthaving become unnecessary is removed through dissolution by use of anorganic solvent.

The organic solvent used in this instance may be, for example, ethyllactate. The substrate is fixed to a spinner and is rotated at 500 rpm,and, in this condition, the solvent is ejected from a nozzle provided ata central portion of the substrate for 30 seconds. Accordingly, thephotosensitive resist is dissolved. Next, the ejection of the solvent isstopped, the rotating speed is raised to 2000 rpm, and rotary drying isconducted for 30 seconds.

The solvent to be used in this treatment is not limited to ethyllactate. Other examples of the solvent include N-methyl-2-pyrrolidine,γ-butyrolactone, cyclopentanone, cyclohexane, isophorone,N,N-dimethylacetamide, dimethylimidazoline, tetramethylurea, dimethylsulfoxide, diethylene glycol dimethyl ether, diethylene glycol diethylether, diethylene glycol dibutyl ether, propylene glycol monomethylether, propylene glycol monoethyl ether, dipropylene glycol monomethylether, propylene glycol monomethyl ether acetate, methyl lactate, butyllactate, methyl 1,3-butylene glycol acetate, 1,3-butyleneglycol-3-monomethyl ether, methyl pyruvate, ethyl pyruvate,methyl-3-methoxypropionate, etc., which may be used either singly or inmixture of two or more of them.

The removal of the residual resist through dissolution can be carriedout by using one of these solvents or a mixture of two or more of them.

Besides, the method for carrying out the treatment is not limited to theabove-mentioned method; for example, a dipping method and the like arealso applicable.

By such a step, a film of the fluorine-containing siloxane resin lowerthan the microlenses ML in refractive index and having good transparencyin the visible region is formed as the protective film 30 on themicrolenses ML. The protective film 30 is so formed that the uppermostsurfaces of convex protuberances of the microlenses ML will not be leftexposed and that the ruggedness at the surface of the microlenses ML isburied. The surface of the thus formed protective film 30 is set to besubstantially flat, and the protective film 30 is provided with openingsin areas where the bonding pad parts are located.

Then, the surface of the protective film 30 formed as above is modifiedby a treatment to enhance its hydrophilicity. As a result, a surfacefilm higher in hydrophilicity than the inside of the protective film 30is formed. The modifying treatment is, for example, activation of thesurface of the protective film 30 by a plasma treatment using anoxygen-containing gas. An example of treating conditions in thisinstance is given below.

Apparatus: Microwave plasma ashing apparatus

Microwave power: 1500 W

Oxygen flow rate: 1000 SCCM

Pressure: 100 Pa

Wafer stage temperature: 35° C.

Treating time: 60 seconds

Consequently, the surface film higher in hydrophilicity than the insideof the protective film 30 is formed at the surface of the protectivefilm 30. The surface treatment conditions are not limited to theabove-mentioned; for example, such a gas as Ar, He, N₂, etc. may beadded to the O₂ gas.

[Process Flow (No. 2)]

FIGS. 6A to 6G are schematic sectional diagrams for illustrating aprocess flow (No. 2) of the method of manufacturing a solid-state imagepickup device according to this embodiment. In the illustration of theprocess flow, schematic sectional diagrams pertaining to the lightreceiving region shown in FIG. 4 are shown on the left side, andschematic sectional diagrams pertaining to the bonding pad region shownin FIG. 4 are shown on the right side.

In the process flow (No. 2), the steps shown in FIGS. 6A through 6E arethe same as those in the above-described process flow (No. 1).Specifically, as shown in FIG. 6A, color filters CF are provided onpixels in a light receiving region. Then, as shown in FIG. 6B, in orderto achieve flattening through burying the stepped portions of thesurfaces of the color filters CF, for example, an acrylic thermoplasticresin is used and a heat treatment is carried out at 180 to 230° C. fortwo to five minutes, to form a second flattening film M2.

Next, a film of a polystyrene-based positive photosensitive resistcontaining diazonaphthoquinone as a photosensitive agent (hereinafter,referred to as “resist”), for example, is formed on the substrate. Theresist is subjected to exposure using the i-line and then todevelopment. Irradiation with UV rays is conducted for enhancingtransmittance, and a heat treatment is carried out, to form microlensesML as shown in FIG. 6C. Incidentally, while formation of the microlensesML by a heat treatment method has been described in this process flow, amethod of transferring a lens shape by an etch-back technique may alsobe adopted.

Subsequently, as shown in FIG. 6D, a protective film 30 is formed in thestate of burying the ruggedness in the surface of the microlenses ML sothat the uppermost surfaces of convex protuberances of the microlensesML will not be left exposed, and that the surface of the protective film30 will be substantially flat.

In this embodiment, like in the above-described embodiment, afluorine-containing resin is used to form the protective film, and,specifically, a fluorine-containing silane compound is used as thefluorine-containing resin. More specifically, the fluorine-containingsilane compound material is preferably a fluorine-containing siloxaneresin, of which the refractive index is lower than that of themicrolenses.

Next, as shown in FIG. 6E, a positive photosensitive resist is applied.As the positive photosensitive resist, for example, a resist containinga novolak resin as a main constituent and diazonaphthoquinone as aphotosensitive agent is used. The positive photosensitive resist issubjected to exposure and development in the state of covering the lightreceiving region and being provided with openings in the areas wherebonding pad parts and the like (inclusive of, for example, scribe linesand the like) are located.

The subsequent steps are different from the steps in the above-describedprocess flow (No. 1). As shown in FIG. 6F, with the above-mentionedphotosensitive resist as a mask, dry etching is carried out to etch awaythe first flattening film M1, the second flattening film M2, and theprotective film 30 formed from the fluorine-containing siloxane resin.In this case, at the time of etching in the areas of the bonding padparts, the etching of the positive photosensitive resist is carried outcontinuously.

Specifically, after those portions of a passivation film which arelocated on the bonding pads are etched away, the etching gas is changedover, and etching of the positive photosensitive resist is carried outcontinuously. More specifically, in the condition where the positivephotosensitive resist is still remaining or after the resist is etchedaway, the etching gas is changed over from SF₆+O₂ to O₂ alone or to anadmixture of O₂ with such a gas as Ar, He, N₂, etc., whereby a surfacetreatment (modification to hydrophilic state) of the protective film 30formed from the fluorine-containing siloxane resin is carried outcontinuously.

This makes it unnecessary to perform removal of the positive resistthrough dissolution in an organic solvent described in the process flow(No. 1) above. Thus, the surface treatment of the fluorine-containingsiloxane resin is carried out in continuity with the step of forming theopenings in the areas of the bonding pad parts, whereby the surface filmis formed. Accordingly, in the process flow (No. 2), the process can beshortened as compared with the case of the process flow (No. 1).

<3. Investigation of Effects of the Embodiment>

After the wafer dicing step, foreign matter of several micrometers insize was observed on the fluorine-containing siloxane regin. Particlesof the foreign matter were subjected to component analysis using an EDX(energy-dispersive X-ray spectrometer), and the foreign matter was foundto be mostly silicon. In general, fluorine-containing resins are knownto be water-repellent. In order to elucidate the water repellencephenomenon and investigate the effects of the surface film in thisembodiment, the contact angle between the surface of thefluorine-containing resin species and water was investigated. Besides,time variation of the contact angle after the surface treatment of thefluorine-containing resin was also investigated.

[Subject Matter Investigated]

Substrate: Wholly flat bare silicon wafer

Fluorine-containing resin species:

(1) Fluorine-containing siloxane resin-1 (refractive index: 1.42)

(2) Fluorine-containing siloxane resin-2 (refractive index: 1.36; aresin obtained by admixing the resin of (1) with silica particulateshaving voids therein)

(3) Fluorine-containing acrylic resin (refractive index: 1.42)

Each of the fluorine-containing resins was applied by spin coating tothe above-mentioned silicon wafer and baked in such a manner that thefilm thickness after the baking treatment was 0.5 μm.

Baking Conditions:

(1) Fluorine-containing siloxane resin-1: 200° C.×5 minutes

(2) Fluorine-containing siloxane resin-2: 200° C.×5 minutes

(3) Fluorine-containing acrylic resin: 200° C.×10 minutes

The surface treatment of the fluorine-containing resins was conductedunder the following conditions.

Apparatus: Microwave plasma ashing apparatus

Microwave power: 1500 W

Oxygen flow rate: 1000 SCCM

Pressure: 100 Pa

Wafer stage temperature: 35° C.

Treating time: 60 seconds

For the fluorine-containing resin species set as above-mentioned,contact angle was measured under the following conditions.

Contact angle measuring method: Contact angle was measured by a waterdrop method with the following parameters.

-   -   Time variation of contact angle was measured without surface        treatment after coating (immediately upon coating, and 20 hr/50        hr/100 hr/200 hr after coating)    -   Time variation of contact angle was measured with        above-mentioned surface treatment after coating (immediately        upon coating, and 20 hours/50 hours/100 hours/200 hours after        coating)

[Investigation Results]

FIGS. 7A and 9B show the investigation results of time variation ofcontact angle under the above-mentioned conditions, in which FIG. 7Ashows the results in the case where no surface treatment was conducted,and FIG. 7B shows the results in the case where a surface treatment (thesurface treatment in this embodiment) was conducted. In the diagrams,time is taken on the axis of abscissas, and contact angle on the axis ofordinates.

The investigation results are as follows.

Samples obtained without surface treatment and subjected to measurementof time variation of contact angle between resin and water, as shown inFIG. 7A, give the following results.

(1) Fluorine-containing siloxane resin-1: stable at about 91°.

(2) Fluorine-containing siloxane resin-2: stable at about 93°.

(3) Fluorine-containing acrylic resin: stable at about 103°.

Samples obtained with surface treatment and subjected to measurement oftime variation of contact angle between resin and water, as shown inFIG. 7B, give the following results.

(1) Fluorine-containing siloxane resin-1: stable at or below 20°.

(2) Fluorine-containing siloxane resin-2: stable at or below 10°.

(3) Fluorine-containing acrylic resin: Tends to rise from about 50° toabout 90°. Specifically 46.4° immediately upon treatment, 49.0° after 20hours, 57.3° after 50 hours, 77.6° after 100 hours, and 91.3° after 200hours.

As seen from the investigation results above, the contact angle for eachof the fluorine-containing siloxane resin-1 and the fluorine-containingsiloxane resin-2 was stable at a value of 10 to 20°. In contrast, thecontact angle for the fluorine-containing acrylic resin showed atendency to rise from 50 to 90° with the lapse of time from immediatelyupon the surface treatment.

The results of visual observation of wettability during the dicingtreatment are set forth in a table shown in FIG. 8. As seen from thetable shown in FIG. 8, water repellency was confirmed for each of theresins, in the state before the surface treatment.

The fluorine-containing siloxane resin-1 and the fluorine-containingsiloxane resin-2 having undergone the surface treatment showed stablewettability, independently of the lapse of time after the treatment. Onthe other hand, the fluorine-containing acrylic resin showed slightwater repellency after 20 hours from the surface treatment, though itdid not show water repellency immediately upon the treatment. After 50hours, 100 hours, and 200 hours from the surface treatment, thefluorine-containing acrylic resin showed a level of water repellencysimilar to that of a fluorine-containing acrylic resin not havingundergone the surface treatment.

From this evaluation and the above-mentioned evaluation results ofcontact angle, it has been found that the wettability of the resinsduring the dicing treatment is lowered starting from a resin-watercontact angle of around 50°.

Thus, though the fluorine-containing acrylic resin showed an effect ofthe surface treatment, the effect was varied with time. In the cases ofthe fluorine-containing siloxane resin-1 and the fluorine-containingsiloxane resin-2, stability of the effect of the surface treatment couldbe secured, as verified by the investigation results.

Where the surface of the fluorine-containing siloxane resin wassubjected to the above-mentioned surface treatment and then to thedicing treatment, no foreign matter was observed on the surface.

FIGS. 9A to 9C shows the surface states upon the surface treatment, inwhich FIG. 9A corresponds to the fluorine-containing siloxane resin-1,FIG. 9B to the fluorine-containing siloxan resin-2, and FIG. 9C to thefluorine-containing acrylic resin. With respect to the surface roughnessobserved under SEM (scanning electron microscope), thefluorine-containing siloxane resin-2 shown in FIG. 9B showed the highestroughness, and the fluorine-containing acrylic resin shown in FIG. 9Cshowed the second highest roughness. The surface of thefluorine-containing siloxane resin shown in FIG. 9A was in the state ofbeing as smooth as can be observed under SEM.

From the above-mentioned fact that the fluorine-containing siloxaneresin-1 and the fluorine-containing siloxane resin-2 having undergonethe surface treatment are higher in hydrophilic nature than thefluorine-containing acrylic resin, it is seen that there is nointerrelation between the surface condition in roughness and thehydrophilicity.

[Elemental Analysis of Protective Film Surface (Surface film)]

In the solid-state image pickup device according to this embodiment, theprotective film has been surface treated to provide the surface film,wherein the protective film and the surface film can be distinguishedfrom each other by fluorine content. Specifically, the surface film islower in fluorine content than the inside of the protective film.

FIG. 10 shows an example of elemental concentration ratio in response tothe presence or absence of the surface treatment of the protective film,for the fluorine-containing siloxane resin. In the table shown in FIG.10, the upper part of the column of treatment corresponds to the sampleobtained without surface treatment, and the lower part corresponds tothe sample obtained with the surface treatment.

The elemental analysis technique adopted here is XPS (X-rayphotoelectron spectroscopy), and, as for the depth direction inanalysis, a material surface (about 10 nm deep) is measured. This yieldssuch information as constituent elements of the material surface and thechemical bond state there.

As shown in the table in FIG. 10, a conspicuous difference in fluorinecontent exists between the case where the surface treatment of thefluorine-containing siloxane resin has not been conducted and the casewhere the surface treatment has been carried out. Specifically, when thesurface treatment was not performed, the fluorine concentration was13.25 atomic %, whereas when the surface treatment was carried out, thefluorine concentration was lowered to 1.94 atomic %. Thus, the surfacetreatment lowers the fluorine content.

Here, the results obtained without surface treatment correspond to theinside of the protective film, and the results obtained with the surfacetreatment corresponds to the surface film in the present embodiment.Therefore, the surface film is lower in fluorine content than the insideof the protective film. Accordingly, enhancement of hydrophilic natureis achieved at the surface film.

<4. Comparison between the Related Art and the Embodiment>

Here, comparison between the solid-state image pickup device describedin Patent Document 3 and the solid-state image pickup device accordingto this embodiment of the present invention will be described.

Patent Document 3 describes that a fluorine-containing silicone resinexcellent in heat resistance is used as the fluorine-containingmaterial, and the surface of the resin is subjected to a plasmatreatment using an oxygen-containing gas. By this treatment,alkyl-modified siloxane bonds —SiO—R (R is an alkyl group) present atthe outermost resin surface are converted into —SiO_(X), so as enhancethe coatability with the positive resist in a subsequent coating stepand the uniformity of the resin layer applied to an upper part thereof.It is also described that it is possible to increase the interfacialadhesion between the fluorine-containing resin material and the resinlayer to be formed thereon.

On the other hand, in the structure of the solid-state image pickupdevice according to this embodiment, no material layer is provided andan air layer is left on the fluorine-containing silane compound to behollow, and the transparent substrate is provide on the upper side ofthe air layer. The transparent substrate is sealed to the package by asealing resin, and, therefore, this structure is different from thestructure of the solid-state image pickup device described in PatentDocument 3.

In addition, the plasma treatment applied to the surface of thefluorine-containing resin in the solid-state image pickup deviceaccording to this embodiment by use of an oxygen-containing gas is aimedat modification of the resin surface. The surface modification heremeans bringing about a change from water repellency (hydrophobicnature), which is a property peculiar to the fluorine-containing resin,to hydrophilic nature.

Patent Document 3 describes that the outermost surface state of thefluorine-containing resin layer is changed from —SiO—R (R is an alkylgroup) to —SiO_(X). In this embodiment, on the other hand, the surfaceof the fluorine-containing silane compound is modified from waterrepellency (hydrophobic nature) to hydrophilicity. This makes itpossible to prevent deposition of silicon swarf or the like during thewafer dicing (cutting) step, and to enhance the yield of the solid-stateimage pickup element. Besides, it is also a characteristic feature ofthis embodiment that materials having no problem as to coatability withthe positive resist applied to the resin are used at the time ofprocessing (opening in the bonding pad areas, or the like) of thefluorine-containing silane compound, and that a plasma treatment usingan oxygen-containing gas is carried out during the processing.

Furthermore, in this embodiment, the contact angle between resin andwater is quantitatively evaluated by the drop method after the plasmatreatment, and time stability of the contact angle (endurance ofhydrophilic nature) and plasma durability (etching durability) in thecase of using an oxygen-containing gas are taken into account. Based onthese, this embodiment utilizes the advantage of using thefluorine-containing silane compound, and, in this point, this embodimentis different from Patent Document 3.

In addition, where microlenses are arranged at the outermost surface ofa solid-state image pickup element, ghost may arise from the surfaceshape and periodicity of the microlenses. Specifically, the lightincident on the solid-state image pickup element through a camera setlens or the like is reflected, as diffracted light, by a periodicstructure (the microlenses). The light thus reflected is again reflectedby an IR cut filter or the camera set lens, to return to the solid-stateimage pickup element.

In the solid-state image pickup device according to this embodiment, theperiodic structure of the outermost surface of the solid-state imagepickup element is eliminated, and the substantially flat protective filmis disposed at the outermost surface. By this configuration, theabove-mentioned diffracted light is reduced, and it is made possible tostably manufacture the solid-state image pickup element.

In this embodiment, the film formed from the fluorine-containing silanecompound lower in refractive index than the microlenses of thesolid-state image pickup element and having good transparency in thevisible region is disposed on the microlenses in such a manner that theuppermost surfaces of convex protuberances of the microlenses are notleft exposed and it surface is substantially flat. In addition, thesurface of the flat film formed of the fluorine-containing silanecompound is subjected to the plasma treatment using an oxygen-containinggas, to modify the surface into a hydrophilic state. As a result, it ispossible to prevent deposition of, mainly, silicon swarf during thewafer dicing (cutting) step, and to realize a good device yield. Inthese points, this embodiment is essentially different from thetechnology described in Patent Document 3.

<5. Examples of Application to Various Microlenses>

The solid-state image pickup device according to this embodiment asabove-described is applicable, irrespectively of the shape ofmicrolenses. Specifically, in order to reduce the ghost which mightarise from the surface shape and periodicity of microlenses, it sufficesthat a low-refractive-index flattening film lower in refractive indexthan the microlenses and substantially flat is disposed in the form ofburying the ruggedness in the shape of the microlenses. For example, thesolid-state image pickup device is applicable not only to the sphericallens shown in FIG. 11A but also to aspheric lenses. Besides, thesolid-state image pickup device can be applied to rectangularmicrolenses shown in FIG. 11B, multi-step rectangular microlenses shownin FIG. 11C, and microlenses utilizing diffraction of light shown inFIG. 11D.

<6. Electronic Apparatus>

FIG. 12 is a block diagram showing a configuration example of an imagepickup apparatus as one example of an electronic apparatus according toan embodiment of the present invention. As shown in FIG. 12, the imagepickup apparatus 90 has an optical system including a lens group 91, asolid-state image pickup device 92, a DSP (digital signal processor)circuit 93 as a camera signal processing circuit, a frame memory 94, adisplay device 95, a storage device 96, an operating system 97, a powersupply system 98, and the like. Among these components, the DSP circuit93, the frame memory 94, the display device 95, the storage device 96,the operating system 97 and the power supply system 98 areinterconnected through a bus line 99.

The lens group 91 functions to take in the incident light (image light)coming from a subject, and to form an image on an imaging plane in thesolid-state image pickup device 92. The solid-state image pickup device92 converts the quantity of incident light forming the image on theimaging plane under the function of the lens group 91 into an electricalsignal on a pixel basis, and outputs the signal as a pixel signal. Asthe solid-state image pickup device 92, the solid-state image pickupdevice according to this embodiment as above-described is used.

The display device 95 has a panel type display device such as a crystaldisplay or an organic EL (electroluminescence) display, and displays amotion picture or still picture shot by the solid-state image pickupdevice 92. The recording device 96 records the motion picture or stillpicture shot by the solid-state image pickup device 92 into a recordingmedium such as a nonvolatile memory, a video tape, a DVD (digitalversatile disk), etc.

The operating system 97, under the user's operation, issues operationcommands as to various functions possessed by the image pickupapparatus. The power supply system 98 appropriately supplies variouskinds of electric power for operating the DSP circuit 93, the framememory 94, the display device 95, the storage device 96 and theoperating system 97, to the respective objects.

Such an image pickup apparatus 90 is applied to camera modules for videocameras, digital still cameras and, further, camera modules for mobileapparatuses such as cellular phones. With the solid-state image pickupdevice according to this embodiment used as the image pickup apparatus92 as above, generation of noise due to unnecessary dust can besuppressed, and an image pickup apparatus capable of producinghigh-quality images can be provided.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2009-118162 filedin the Japan Patent Office on May 15, 2009, the entire content of whichis hereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1-7. (canceled)
 8. An electronic apparatus comprising: a solid-stateimage pickup device; and a signal processing unit operable to process asignal based on an electric charge produced by the solid-state imagepickup device; wherein the solid-state image pickup device includes asolid-state image pickup element operable to produce an electric chargeaccording to the amount of light received; a lens disposed on the upperside of a pixel of the solid-state image pickup element; a protectivefilm which covers the upper side of the lens and a surface of which isflattened; and a surface film which is formed at the surface of theprotective film and which is higher in hydrophilicity than the inside ofthe protective film.